In the wake of developments for electric automobiles and hybrid drives for vehicles having a combination of internal combustion engines and electric motors, very high demands are made of batteries for future automotive generations with regard to the lifetime of the energy content and efficiency. To meet these demands, many types of batteries have active cooling, by using a coolant, a refrigerant or air, for example. In the case of batteries such as lithium ion batteries, it is also frequently advisable to provide waste heat utilization or the option of preheating the battery. To do so, it is usually advantageous to provide thermal insulation for the battery to reduce thermal losses. Furthermore, batteries in vehicles have a reinforced housing to reduce the risk to occupants in the event of an accident or damage. For this reason, batteries are therefore often accommodated in encapsulated, thermally insulated housings.
Some types of batteries, for example, lithium ion batteries have a very high energy density, which is associated with the disadvantage that relatively large quantities of energy are stored in a very small space, so that very intense reactions may occur under some circumstances. Critical reactions may usually be extinguished or brought to a standstill by cooling to a temperature below a limiting temperature. If a battery such as a lithium ion battery, for example, is installed in a vehicle body in an encapsulated, thermally insulated housing, virtually no extinguishing or cooling of the battery from the outside is possible anymore because of the construction which encases and insulates the battery.
Batteries having a very high power density using the lithium ion batteries in question here are increasingly manifesting the phenomenon of thermal coupling. The phenomenon of thermal coupling is understood to mean that a battery which has exceeded a critical temperature once will continue to heat up until the battery is dead. However, in a very early phase of this phenomenon, also known as “thermal runaway,” it is still possible to prevent such a thermal runaway by very rapid and intense cooling. This cannot be achieved by cooling with air or water because the design of the cooling system is not practical for such rapid and intense cooling of high thermal masses to prevent a thermal runaway, in particular of a lithium ion battery.
In summary, it may be concluded that the safety problem presented here is a main obstacle in the commercialization of such batteries.